According to British Royal Message Board, it seems the Duke and Duchess of Cambridge will attend the state banquet. So the apparent answer is yes to your question, Gert-Jan. See the link....
--Previous Message-- : Will Kate attend the statebanquet? : : --Previous Message-- : : Let's have a poll on the tiara Kate might : wear to the State Banquet in October for the : President of China. : : I know there is a large pool to choose from : but these I feel would be the most likely. : : : : : : :